Cycloalkenes by intramolecular wittig reaction

Methods of preparation of phosphorus ylides substituted at the carbon atom of the P=C group with atoms of various elements and their application in organic synthesis are systematised and generalised The bibliography includes 508 references

https://iopscience.iop.org/article/10.1070/RC1997v066n03ABEH000232/pdf

Methods of preparation of C-substituted phosphorus ylides and their application in organic synthesis

Ein neues Jahrtausend hat begonnen – Grund genug, sich die Frage zu stellen, welchen Stand die Totalsynthese von Naturstoffen erreicht hat. Dieser Aufsatz mochte eine Antwort geben, indem er die Entwicklung dieser chemischen Disziplin, die Aspekte von exakter Wissenschaft und schoner Kunst in sich vereint, von Anbeginn bis in die heutige Zeit beschreibt; es wird geschildert, wie viel wir in der Wissenschaft der Totalsynthese schon erreicht haben, aber auch, dass dieses Forschungsgebiet den Kinderschuhen gerade erst entschlupft.

Der Stand der Totalsynthese zu Beginn des 21. Jahrhunderts

Described in this article are studies of structurally novel [3.2.0]bicyclic β-lactam ring systems that are isomeric to those of the penicillin, penem, and clavulanic acid families of antibiotics, but which have the lactam functionality arranged in alternative orientations within the four-membered ring. Semiempirical calculations indicate that the thermodynamic stabilities of the three alternative isomeric ring systems are similar to that of the classical penam or penem structure, and ab initio methods reveal that the LUMO energies of the two C-fused ring structures 11 and 12 are more than 1 eV lower than that of 2-azetidinone, but 0.22 to 0.73 eV higher than that of the penem ring 13. The LUMO energy of the N−S fused penem structure 14 is about 0.2 eV lower than that of 13. These studies also suggest that the N-fused bicyclic β-lactams are considerably more electrophilic than the corresponding C-fused compounds. Several of the new heterocyclic rings were synthesized using a two-step cyclization strategy t...

Studies on Nonconventionally Fused Bicyclic β-Lactams

Effects of a highly conserved hydrogen bond between the distal histidine (His) and a nearby asparagine residue (Asn) of peroxidases upon the active site structures were investigated using resonance Raman (RR) and EPR spectroscopy. Although there is no crystallographic data for horseradish peroxidase (HRP), Asn70 is deduced to be the hydrogen bond acceptor for HRP. Accordingly, site-directed mutagenesis of Asn70 to Val (N70V) and to Asp (N70D) was carried out with HRP, and their RR spectra were compared with those of native and wild type (WT) enzymes in the resting, reduced, CN-bound ferric and compound II states. In the resting state, the six-coordinate high-spin structure is the main component for N70V and N70D mutants, while the five-coordinate high-spin structure is dominant for the native and WT HRPs. This was confirmed with EPR spectra. The FeIII−CN stretching (νFe-CN) and bending RR bands of the linear and bent forms were identified using 12C15N and 13C14N isotopes. The νFe-CN frequency of the linea...

Effects of Concerted Hydrogen Bonding of Distal Histidine on Active Site Structures of Horseradish Peroxidase. Resonance Raman Studies with Asn70 Mutants

K. Prasad

Papers

The penems, a new class of .beta.-lactam antibiotics. 2. Total synthesis of racemic 6-unsubstituted representatives

THE PENEMS, A NEW CLASS OF β-LACTAM ANTIBIOTICS. 6. SYNTHESIS OF 2-ALKYLTHIOPENEMCARBOXYLIC ACIDS